Refrigeration system with multiple fluid heat transfer



C. BOLING Nov. 10, 1953 REFRIGERATION SYSTEM WITH MULTIPLE FLUID HEAT TRANSFER Original Filed July 27-, 1950 4 Sheets-Sheet 1 INVENTQR cecal ,Bolz BY M 'ATTORN Nov.'10, 1953 c. BOLING REFRIGERATION SYSTEM WITH MULTIPLE FLUID HEAT TRANSFER 4 Sheets-Sheet 2 Original Filed July 27, 1950 m l mm m. Un vm fl fl mBQ/ N JR mw om QN Q r@ i l F \@N M. mm m w N9 mm. mm mm mm #8 Wm w M @w I m? @w Nw wN UN NW wm 5 v r l mm 3 l Q @N 1 mm 5 Na 3 on Q g 8 E H NN. 3mm Q'J mm W10. QIQ l Ml a J I l R m6 3 QM mwmlL g m QM QR; @W QN N m L mi g JPJVENTOR C eczl B 0 ATTORNEYS Nov. 10, 1953 c. BQLlNG 3 REFRIGERATION SYSTEM WITH MULTIPLE FLUID HEAT TRANSFER Original Filed July 27, 1950 4 Sheets-Shed 3 L l 38 UKQI' F E 64 '5;- 56 :1 @v

INVENTOR gecil ,Bolin ATTORNEY Nov. 10, 1953 c. BOLING 2,658,358

REFRIGERATION SYSTEM WITH MULTIPLE FLUID HEAT TRANSFER Original Filed July 27, 1950 v 4 Sheets-Sheet 4 N3 Q N i 3 5 96;

TTTB.

INVENTOR Cec it Bolin Y ATTORNEYS Patented Nov. 10, 1953 REFRIGERATION SYSTEM WITH MULTIPLE FLUID HEAT TRANSFER Cecil Boling, Brewster, N. Y., assignor to The Heat-X-Changer 00., Inc., Brewster, N. Y., a corporation of New York Original application July 27, 1950, Serial No.

UNITED STATES PATENT OFFICE 176,128, now Patent No. 2,611,587, dated September 22, 1952. Divided and this application November 14, 1951, Serial No. 256,204

cation Serial No. 176,128, filed July 2'7, 1950, now

Patent No. 2,611,587, September 23, 1952, and the claims of which are now restricted to the heat interchange tube and fin structure.

An object of this invention is to provide improved refrigeration systems wherein extremely eflicient operation is obtained with equipment which is simple and sturdy in construction, inexpensive to manufacture and maintain, compact, light in weight and thoroughly dependable in use, and which is adaptable to meet many problems in different fields. Further objects are to provide improved heat exchange units having certain or all of the above desirable characteristics with particular attention being directed toward providing improved condensers, evaporators and the,

like. A further object is to provide heat exchange equipment which may be of more or less standardized design and construction and yet which is adaptable for use in solving many different problems which have been encountered in widely diversified fields. A still further object is to provide for the manufacture of equipment of the above character upon a mass production basis with the advantages and economies which may be obtained thereby. These and other objects will be in part obvious and in part pointed out below.

Theinvention accordingly consists in the features of construction, combinations of elements, arrangements of parts and in the several steps and relation and order of each of the same to one or more of the others, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the drawings:

Figure 1 is a somewhat schematic representation of one embodiment of the invention;

Figures 2 and 3 are similar to Figure 1 but show other embodiments of the invention;

Figure 4 is an enlarged view with parts broken away of the condenser of the embodiment of Figure 2;

Figures 5 and 6 are vertical sections, respectively, on the lines 55 and 66 of Figure 4;

7Claims. (Cl.62117.55)

Figure '7' is a section on the line l-l of Fig- Figure 8 is a further enlarged view on the line 8.8 of Figure 4; I

Figure 9 is a view similar to Figure 4 butshowing a heat transfer unit of the embodiment of Figure 1; and,

Figure 10 is a section on the line |o- |o of.

Figure 9.

Refrigeration systems generally include two or more heat transfer units wherein heat is transferred to or from a stream or streams of the refrigerating medium. Examples of such heat transfer units are: condensers, evaporators and h at interchangers Where one stream of refrigerant i passed in heat transfer'relationship with another or where a liquidor air is cooled or heated by a liquid or gas. With any particular refrigeration system the performance may be improved by increasing the rate of heat transfer, at the heat transfer units. Thus, if there is a high. rate of heat transfer at the condenser, a rela-. tively large amount of refrigerant is condensed with a minimum amount of 'air or water and with a relatively small condenser. Similarly, the per- Generally, the performance of an air cooled.

condenser varies over a relatively wide range in accordance with the ambient temperature as well as the load. That is, the rate at which heat is transferred from the condenser drops materially when the ambient temperature rises, and it has been accepted practice to design air cooled condensers for refrigeration systems with a relatively high excess load factor at normal or mean ambient temperatures solely to take care of the high loads at high ambient temperatures. Proposals have been made to provide both an air-cooled condenser and a water cooled condenser for a single refrigeration system or to utilize both air and water to cool a single condenser unit. With such arrangements most or all of the heat is passedto the air at light loads and at low ambient temperatures, but as the ambient temperature orthe load rises, heat is passed to the water. However, it has been difficult to provide for the efficient transfer of heat to both air and water with condenser structure which is inexpensive to manufacture and thoroughly satisfactory in every respect.

A similar problem arises with evaporators aesaasa 3 where it is desirable to provide a good heat transfer relationship between the refrigerant and air at the evaporator surfaces for the purpose of cooling the air, and also between a defrosting medium and the evaporator surfaces for the purpose of melting the frost free during a defrosting operation. Similarly, with a combination air cooling and heating system where a refrigeration system cools a building in summer and heating is provided in winter, it is desirable to provide a single heat transfer unit of minimum size and cost in each room which isthe heat radiator in winter and the cooling or heat absorbi'ng unit in summer. In each of the systems referred to above, the present invention contemplates the provision of one or more heat transfer units; each of which is adapted to pass two or more fluids, 1. e., liquids or gases, into efficient heat transfer relationship with each other orto pass selectively or simultaneously two such fluids into heat transfer relationship with air or the like.

Referring particularly to-Flgure 1 of the drawings wherein a refrigeration system is shown somewhat schematically, a compressor 2 is driven by a motor 4 and is automatically controlled so that it compresses refrigerant and delivers it through a hot gas line 5 to a primary condenser 6 and thence to a secondary condenser I. The refrigerant is condensed in the condensers and the liquid refrigerant goes to a receiver 8' and thence through a liquid line III and an expansion valve l2 to an evaporator H. The refrigerant evaporates in the evaporator and flows through a line I! which has a throttle valve I9 therein which does not interfere with the flow of the refrigerant gas during the refrigeration cycle. The refrigerant then passes through a heat exchange passageway in the secondary condenser I, and a line it tothe compressor;

During normal operation frost accumulates on evaporator l4 and the evaporawris defrosted by passing hot gas from the compressor directly to the evaporator so that it does not flow through the condensers. Accordingly, the system is provided with a valve I! in a bypass line 18, and this valve is opened to connect the hot gas line 5 through line I8 to the inlet of evaporator l4; the hot gas heats the evaporator and the ice is melted free. The rise in pressure causes the throttle valve l8 to close and throttle the flow of refrigerant as it returns from the evaporator to the compressor through line ii to the heat exchange passageway in the secondary condenser 1 and thence to. the compressor. through line It. This causes the refrigerant to condense in the evaporator and'it is evaporated in the secondary condenser I so that the secondary condenser is also a re-evaporator.

In the embodiment'of Figure 2 the system represented is similarto that of-Figure 1' except that: a special evaporator i9 is provided; a condenser 2| of modified form replaces the condensers 6 and 1; and, the bypass line l8 and valves l1 and I! are omitted. In this embodiment'the defrosting operation is carried'on by passing. a hot liquid through a separate passageway in the evaporator to perform the defrosting operation. Consequently, no hot gas is passedto the evaporator, and it is unnecessary to provide. for the re-evaporation of refrigerant passing to the compressor.

Condenser2 I is of a special constructionwhich constitutes an important phase of the invention and now will be describedmore in detail. This condenser is-shown in Figures 4-to 8and com prises a set of six horizontal multiple-passageway condenser tube assemblies 20 (Figure 4) rigidly mounted and interconnected at their ends by a pair of header assemblies 22 and 24. Each of the condenser tube assemblies 20 comprises an outer tube 26 and an inner tube 24 (see also Fisure 8), having an internal, radially-compressed. fin assembly 30 positioned in the annular space 82 between the two tubes. In each tube assembly the refrigerant from the compressor passes through the space 32 which acts as a condensing passageway where the gas is cooled thereby to condense it toa liquid.

Cooling water is flowed through the passageway 34 in each inner tube 28 so that cooling of the refrigerant gas is obtained as a result of heat passing through the inner tube wall to the water. The new of water is controlled by a metering valve 28 which is connected through a pressure tube to the compressed or hot gas line from the compressor and permits water to flow through the condenser at a rate suflicient to keep the pressure of the compressed gas within desirable limits.

The header assemblies 22 and 24 (Figure 4) provide rigid support for the condenser tube assemblies and are in turn supported at the bottom (see also Figures 5 and 6) by a pair of sheet metal mounting brackets 23 which are clamped in place on the base of the machine by bolts (not shown). The header assemblies provide fluid connections whereby the various passageways 32 are connected in series; and, at the same time, all of the passageways 34 are connected in series. Accordingly, header assembly 24 is provided at the bottom with a water inlet fitting 35, and at the top with a water outlet fitting 38; and (see Figure 5), there is at the top a refrigerant inlet fitting 21 and at the bottom a refrigerant outlet fitting 84.

Header assembly 24 is formed by two interengaged vertical channels 40 and 42 (see Figure 7) and a third enclosing channel 44. Channels 40 and 42 form the header passageways for the inner tubes 28 while channels 42 and 44 form the header passageways for the annular passageways 32 in tubes 28. Accordingly, channel 42 is provided with a set of flanged openings 48 which receive the ends of tubes 28 and channel 44 is provided with concentrically positioned flanged openings 48 which similarly receive the ends of tube 26. Referring to Figure 6, the space be tween channels 48 and 42 is divided into four header passageways 50, 52, 84 and 56 by flve arch-like transverse walls 58, 88, 82, 84 and 68 which are positioned as shown in Figure 6 and provide horizontal blocks or walls between the respective header passageways. The header passageways 50 and 58 are open respectively to the ends of the top and bottom tubes 28 while each of passageways 52 and 54 is open to the ends of a. pair of the centrally positioned tubes 28 (see also Figure 4). Referring to Figure 5, the header passageways 84, ll, 12 and 14 between channels" and 44 are similarly formed by archlike transverse walls I8, 18, 80, 82 and 84. The top and bottom passageways 88 and HI are connected respectively to the annular passageways 32 in the top and bottom tube assemblies while the passageways l0 and 12 are each connected to a pair of the centrally positioned passageways 22.

Referring to the left-hand portion of Figure 4, header 22 is substantially identical in construction with header 24 except that arch-like transverse walls 86 and 88 are positioned to provide: header passageways", 82 and 94 which connect the annular passageways 22 in the lower pair of tubes, the central pair of tubes, and the top pair of tubes, respectively; and header passageways 96, 88 and I which connect the ends of the lower pair of tubes 28, the central pair of these tubes, and the top pair of these tubes, respectively. It is thus seen that the water inlet fitting 35 is connected to a water passageway which extends through passagewaySB, the lower tube 28, passageway 96, the next tube 28, passageway 54, the next tube 28, passageway 98, the next tube 28, passageway 52, the next tube 28, passageway I00, the top tube 28, and thence through passageway 50 to the water outlet fitting 36. A similar refrigerant circuit is provided from the refrigerant inlet fitting 31 at the top and through passageways 68, 32, 84, 32, I0, 32, 92, 32, I2, 32, 90, 32, and I4 to the refrigerant outlet fitting 38. Each of the channels 40 is provided witha set of flanged openings I02 which are respectively in alignment with the ends of tubes 28 and each of these openings is threaded; and thewater inlet and outlet fittings are threaded into the top and bottom of these openings I02 and the other of these openings are closed by a screw cap I04. Thus, the water circuit may be readily cleaned by removing these fittings and screw caps, and by inserting a spiral tube cleaner.

The various elements of the header assemblies are connected to each other and to tubes 26 and 28 by a soldering operation. Thus, during manufacture the elements are assembled jig, and the headers are then heated and soldered. Upon cooling the entire unit is held together as a unitary structure, and the joints and seams are sealed.

The fin assembly 30 is of the type disclosed in my copending application Serial No. 17,899, filed March 30, 1948, now Patent No. 2,611,585 September 23, 1952, and is characterized by being formed of sheet metal which is somewhat corrugated so that fins are provided extending longitudinally of the tubes. Referring particularly to Figure 8, each of the fin assemblies 30 comprises a single piece of sheet metal which is of substantially the exact length as tube 28 and is corrugated to form an even number of substantially fiat radial fin portions I08 which, except at the edges of the sheet, are connected each with the next two. The fin portions are connected adjacent tube 28 by a relatively sharp angle bend I I0 and adjacent tube 26 by a rounded bend II2.

This gives a good heat transfer relationship with both tubes, and gives structural advantages. During construction of the apparatus, the fin assembly 30 and the inner tube 28 are slid into tube 26, and tube 28 is then expanded so that it presses radially outwardly upon the fin assembly 30. Thus, each of the fin portions I08 is com: pressed radially so that one edge is pressed at a bend I I0 against the outer surface of tube 28 and the other edge is pressed at a bend II2 against the inner surface of tube 26. With this construction the fin assembly is expansible so that it is pushed by the inner tube outwardly against the outer tube, but can not be compressed to any great extent radially and, therefore, the fin assembly is placed under radial compression by the expansion of tube 28. Thus, the fin assembly has good heat transfer relationship with both of the tubes and also with the refrigerant flowing through the passageway 32 between thetubes.

Furthermore, the refrigerant flow through this passageway is relatively unobstructed because the fins extend longitudinally of the passageway.

In Figure 2 the evaporator I9 is substantially identical in construction with the condenser 2I,

in a

except that each of the tube assemblies has on its outer tube II3 a fin assembly of the tube II5 formed by square sheet metal fins II I. These fins III are put in place on each tube II3 prior to assembly with its internal fin assembly 30 and its inside tube 28, and the tube I I3 is expanded to hold the fins I I I in place and to give a good heat transfer relationship. The refrigerant passes from the receiver 8 through line- I0 and expansion valve I2 to the refrigerant inlet fitting Hi. It then flows through the series of evaporator passageways identical with passageways 32 to the refrigerant outlet fitting II6 from which it returns through line I5 to the compressor. An inlet fitting II8 identical with fitting 36 on the condenser provides an inlet connection for a defrosting liquid which may be an aqueous solution or another liquid which is heated.

Thus, when frost accumulates on the evaporator the refrigerationoperation is discontinued and heated defrosting liquid is supplied to fitting H8. corresponding to the water passageway in the condenser and it is discharged at the bottom of the evaporator, through a fitting I23. The heat from the defrosting liquid passes through the walls of tubes 28 and thence through the fin assemblies 30 to the outer tubes 26. This heats the outer tubes and the fins so that the accumulated frost or ice is melted free. It is thus seen that the evaporator surfaces are in good heat transfer relationship with the inside tubes 28 and, therefore, the defrosting operation is carried on efficiently. This good heat transfer relationship exists by virtue of the fin assemblies 30 being held underradial compression so that each fin assembly is in tight contact with the outer surface of its inner tube and the inner surface of its outer tube. V I

Referring now again to Figure 1, it was stated above that the secondary condenser I is of special construction and provides a heat transfer passageway for the return refrigerant. Referring to Figure 9, this condenser I is in many respects identical with condenser 2I of Figure 2. There are six tube assemblies I2I, each of which is constructed in the same manner as tube assemblies of Figure 2 but the outer tube 26 carries a fin assembly I22 formed by fins I 23 which are identical with the fins II! on the evaporator of Figure 2. The headers I24 and I25 are quite similar to the corresponding headers 22 and 24 of Figure 2 and differ only in that certain of the partitions or transverse walls are omitted and the right-hand header I25 is cu away at the top.

Header I25 is formed by a set of interengaged channels I26, I28 and I30 and-there is a single passageway I32 at the right between channels I26 and I28 which is open to the right-hand ends of all of the tubes 28, except for the top tube. There is also a single passageway I34 between channels I28 and I30 which is open to the annular finned passageways 32 between the concentric tubes 26 and 28 of the respective tube assemblies. Header I24 is similar to header I25 except that its channels extend to the top of the condenser and provide a single passageway I36 which is open to the left-hand ends of all of the tubes 28 and a passageway I38 which is open to the left-hand ends of all of the passageways 32.

It has been pointed out above that (see also Figure l) the compressed gas fiows from the compressor to the primary condenser 6 which, in actual construction, is mounted at the side of This liquid flows through the passageway 1.. the secondary condm'ser land-a single fan passes air through the two condensers. The refrigerant from the primary condenser passes: through two tubes I andllt to' the upper portion ofpassageway I28 at theleft-hand end o'f' the secondary condenser and, as indicated, this passageway is open to the ieft-hand'end-of all of the annular finned passageways 32 in the various tube assemiiliesi The bottom of this passageway I38 is connected through a line I to the receiver and, tnerrore; the condensed refrigerant from the primarycondenser'fiows through the lines I and I42 into passageway I38 and down' this passageway and through line I to the receiver with minimum resistance to flow. However, any refrlgerant gas which-is not condensed in the primary'condenser sseparates from the liquid refrigerant in passageway I38 and flows into the various passageways 32 where heat is passed from it by the internal fin assemblies 36 and also by contact with the outer tubes 26.

The internal fin assemblies 30 are compressed as a result of' the expansion of the internal tubes 28 during assembly and the external fins I23are in good-heat transfer relationship with their tube surfaces. Thus, the heat from the refrigerant gas passes efliciently to the fins I23 and thence to the'air. The right-hand ends of the passageways 32' are also interconnected by the passageway I84 and liquid refrigerant flows from passageway I to the left to passageway I88; therefore, noliquid is trapped in any of the passageways. Thus, an efficient condensing action is performed-by the secondary condenser.

The secondary condenser is also a re-evaporator and the refrigerant returns through it from the evaporator to the compressor. This return re-evaporator passageway is formed by the inside tubes 28 and the interconnecting passageways lfl'and I36. Line II is'connected'to the bottom of passageway I32 at the right-hand side of the unit and the top tube "has-its right-hand end connected to line I6 which extends to the intake port of the compressor. As indicated above, passageway I82 is connected to the righthand end of all of tubes 28 except the top one and the left-hand passageway I 36 is connected to all of the tubes 28. Thus, the refrigerant flowing from line I6 into passageway I32 flows freely to the left through the five lower tubes 4 28 and into passageway I36. From passageway I38 the refrigerant flows to the right through the top tube 28 which is of sufficient size to carry the refrigerant Without objectionable pressure drop. Thus, the refrigerant returning from ,the evaporator to the compressor during the refrigeration cycle is passed into heat exchange relationship with refrigerant on the high side. This not only insures that no drops or slugs of liquid refrigerant will reach the compressor in the return line but it also improves the performance of the system.

During the defrosting cycle the flow from the evaporator to the compressor is unchanged and, as indicated, hot gasflows through line I8 directly to the evaporator where it melts ice or frost free. During this operation refrigerant is condensed in the evaporator and this flows through line II and valve I8, which then provides a pressure drop to passageway I82 and thence through the lower five tubes 28" to passageway I36. The liquid refrigerant tends to flow through the lower tubeswhile the upper tubes tend to remain free for gas and vapor. Heat, however, is passed to the refrigerant through'the walls of tubes 28 from the respective fin blies I 88. These iin ass'emblies are ingood heat exchange relationship with the outer tubes "and the external flns I23. Therefore, heat is absorbed by the fins I28 and passed by the internal fin: assemblies to the refrigerant in the inner tubes". The unit therefore acts-as an emcient re-evaporator and insures the evaporation of all liquid refrigerant which flows from the evaporator. The five tubes 280perate in parallel and; as indicated, they offer minimumresistanceto the refrigerant flow. The top tube 28 prevents "slapping over" which might occur under scmeconditions of operation if line I6 were connected to passageway I36; Under some circumstances there may be one or more additional tubes connected in parallel with the top tube'or a moreextended series arrangement maybe provided so'that the refrigerant follows a longer path;

In'the embodiment of Figure 3' an arrangement is shown schematically wherein a single heat transfer unit I acts as an evaporator in the summer to cool-the air in a room, for'exampls, andacts'as a heat radiator in the winter to heat the room. The unit Illis identical with'evaporstor I9 of Figure 2an'd the parts are correspond-- ingly numbered; However, when the unit is setingas anevaporator: its surface temperature is abovefreezing and therefore frost does not form audit is unnecessary'to defrost it.

For purposes of heating in winter the inner tubes "of unit I88 areoonnected to a heating medium, illustrativoiy, steam supplied from a remote boiler I". The condensing unit of Figure 3' is identical with that of Figure 2 except that an air and'water'cooied condenser I is provided which is identical in structure with evaporators' I8 and III; In condenser I the inner'tube circuit, formed by'tubes 28 connected m series; acts as a water circuit for the condenser cooling water the same as in Figure l and therefore wateri's supplied to this'inner tube circuit through a valve I66 identical with valve 28 of Figure 2.' However, each of the condenser tube assemblies is provided with external fins as in Figure l', and under low load: conditions and at low ambient temperatures, the cooling effect of the fins is suflicient to condense all of the refrigerant'. Under such circumstances, valve I remains closed and there is no water flow because the pressure of the hot'gss does not rise. However, athigh loads and when the ambient temp'erature rises the"high side" pressure rises indicating'that the condenser is not condensing all of the refrigerant; this-opens valve I and permits water to fiowthnough the condenser so that there is auxiliary cooling. with this arrangemeat It has been found that the unit can be designedfornormal-operation as a solely air cooled unit; and yet'peak and abnormal loads need not be taken into consideration insofar as the air cooling surface is concerned because such loads are handled with the assistance of water cooling. This arrangement is of particular advantage under circumstances where the'free use of water is objectionable and where maximum efficiency Is important.

With the embodiment of Figure 3 the refrigeration system operates to cool the air during warm weather in accordance with the normal refrigeration cycle of operation. During, such operation the inner tubes carry no heating or cooling medium. However, they perform the function referred to previously of providing the high heat transfer relationship between the fin structures 9 and the outer tubes and thence with the air. When cooling is no longer required the refrigeration system is turned off and, if desirable, heating may be effected immediately by merely supplying the heating medium such as steam to the inner tube circuit. The steam or other heating medium such as hot wa er flows through the inner tube circuit and the heat is transferred through the walls of tubes 28 and thence through the internal fin assemblies to the outer tubes 29 where it is transferred to the air. It is thus seen that the refrigeration system and the heating system utilizes the same heat transfer structures and yet the cooling fiuid and heating fiuid circuits are not interconnected. In Figure 3 the schematic representation is of a system having one heat transfer unit I43, although it should be clearly understood that such a system would normally include several, if not many, such units.

With the condenser I425 it should be noted that maximum performance is obtainable with a minimum sized condenser because the compressed internal fin assemblies make it possible to provide a, high rate of heat transfer with the air as well as with the Water. Similarly, in the heat transfer unit I43 high heat transfer is provided between the refrigerant and the air in the summer and also between the steam and the air in the winter. Thus, a single heat transfer unit of minimum size may be provided with a single air circulating and mounting structure. Under some circumstances hot water or other hot fluid may be used as the heating medium and the fins may be omitted if the external surface is sufficient otherwise. Generally, the heat transfer units of the type herein disclosed are provided with fans when there is to be a heat transfer relationship with air. Thus, in the embodiments shown, fans are used whenever the tube assemblies are provided with external fins.

With the various heat transfer units herein disclosed it will be appreciated that the header structures may be modified to obtain either full parallel or full series flow, or there maybe corn bined parallel and series fiow. For example, with a condenser the inner tubes may be connected to operate with adjacent pairs in parallel or all of them may be in parallel. Similarly, the passageways 32 may be connected so that two or three are in parallel. The particular internal fin structure gives minimum pressure drop through the passageways 32 even though there is rapid flow. The pressure drop is, of course, reduced if parallel flow is provided, although under some circumstances, it is desirable to provide an extended series fiow.

The arrangement of providing the internal fin Structures 30 with U-bends of greater mean radius at the outer tubes than at the inner tubes is an important feature of construction. This characteristic of the fin structures is obtained by corrugating sheet metal with alternate wide and narrow U-bends. Thus, in actual production, a strip of sheet metal having a width or transverse dimension which is exactly that desired as the length of the fin assembly is placed in a fin-forming machine. This fin-forming machine has a sheet holder adjacent a forming zone at which the sheet is clamped originally with a leading edge projecting into the zone. Two forming strips of different widths are positioned on the opposite sides of the projecting leading edge of the sheet and they are moved edgewise into engagement with the opposite sides of the sheet.

The engagement of the two forming strips is 10' along zones spaced slightly from each other and the movement of the forming strips is continued so that the sheet is formed into two corrugations. One of the corrugations is narrower than the other because its forming strip is narrower and one U-bend is also. narrower than the other.

The forming strips are then withdrawn and then the sheet is advanced and the operation is then repeated until there is a sufiicient number of corrugations for a fin assembly 30. The fin assembly is then curved into annular form and the edges are interlocked as shown. An inner tube 28 and a fin assembly 30 is then inserted into atube 26 and in this embodiment theinner tube 28 is expanded. The expansion is sufiicient to pressthe fin assembly 30 outwardly against the inner wall of tube 26 and each corrugation or fin portion is placed under compression. Under some circumstances the outer tube may be deformed to a smaller size to obtain this compressed condition of the fins. The internal fin assembly is deformable so that its mean radius may be changed readily or it may even be deformed to a non-annular shape so as to conform to theexact radial dimensions of the space provided for it. Such deforming changes the total angles of the various Ubends but the radially extending fin portions are not bent materially. Thus, the fin assembly will still withstand substantial radial compression which, in any event, is made sufficient to insure the desired heat transfer relationship with the confining walls. This high heat transfer relationship is thus obtainable without the use of solders or other bonding metals or auxiliary structures. In the illustrative embodiments,tubes 26 and 28 and internal fin assemblies 30 are copper, although it is understood that other metals may be used when desirable.

As many possible embodiments may be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from thescope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. Ina refrigeration system of the character described wherein refrigerant is passed to an evaporator in liquid phase and returns in gas phase, the combinationwith the other components of said system of a heat transfer unit connected in flow series in the refrigerant circuit which comprises, a bank of parallel tube assemblies each of which is formed by an inner tube and an outer tube which are concentrically positioned to provide an annular space therebetween and an annular fin assembly formed by sheet metal which has been corrugated with each corrugation forming a fin portion which extends somewhat radially and bridges said annular space, said fin assembly having the characteristic that it is deformable but is capable of withstanding radial compression, said tubes being of such relative size as a result of one of them being deformed after assembly that said fin assembly is compressed within said annular space whereby it exerts substantial pressure upon theouter surface of the inner tube and the inner surface of the outer tube, and a pair of headers for said tube assemblies and providing fluid connections to said annular spaces thereof and also to the inner tubes thereof, each of said header assem 11 blies including a first wall portion which provides rigid mounting means for the various outer tubes and a second wall means which provides mounting means for the various inner tubes.

2. Apparatus as described in claim 1 wherein said heat transfer unit is a condenser and reevaporator unit wherein, said header assemblies comprise means connecting a plurality .of said inner tubes in parallel whereby refrigerant flowing from the evaporator is provided with a plurality of parallel paths of flow, and which includes external fin assemblies mounted respectively on said tube assemblies.

3. Apparatus as described in claim 2 wherein said refrigeration system includes a primary condenser and said heat transfer units acts as a secondary condenser, and wherein said header assemblies connect all of said annular spaces of the tube assemblies in parallel relationship.

4. Apparatus as described in claim 1 wherein each of said annular fin assemblies has its corrugations connected by relatively narrow U-bends adjacent the inner tube with which it is associated and connected by substantially wider U- bends adjacent the outer tube with which it is associated.

5. Apparatus as described in claim 1 wherein said annular spaces in said tube assemblies comprise the evaporator for the system, and wherein heat is supplied to the unit through the central passageway through said tubes. I

6. In a refrigeration system of the character described wherein refrigerant is compressed and is condensed after which it i returned to the compressor, the combination with the compressor and the evaporator of, a condenser and re-evaporator unit connected in flow series in the refrigerant circuit, said unit including a plurality of tube assemblies each of which is formed bya pair of concentrically positioned tubes having a condensing passageway therebetween and a radially compressed fin assembly positioned within the condensing passageway and having good heat transfer relationships with the two tubes by virtue of the compressed condition of the fin assembly, said unit including a pair of header assemblies which include means connecting one or more Of the inner tubes of the tube assemblies in series relationship in the return path of the refrigerant flowing from the. evaporator to the compressor whereby liquid refrigerant which flows from the evaporator is re-evaporated by heat passing to it through said fin assembly, each of said header assemblies including first wall means which provide rigid mounting means for the inner tubes and second wall means which provide rigid mounting means for the outer tubes.

7. In a refrigeration system of the character described wherein refrigerant is compressed and is condensed, and is then passed to an evaporator where it is evaporated, after which it is returned to the compressor, and wherein frost or the like tends to accumulate on exposed surfaces of the evaporator which frost or the like must be re-' moved by a defrosting operation, the combination with the compressor and the other components of the system of an evaporator formed by a plurality of tube assemblies and a pair of headers providing mounting means for said tube assemblies and providing for fluid flow therethrough. each of said tub assemblies comprising a pair of concentrically positioned tubes of different radii and having an annular passageway therebetween and a central passageway through the smaller diameter tube, said assembly also having a radially compressed fin assembly positioned within said annular passageway and having good heat transfer relationships with the two tubes by virtue of the compressed condition of the fln assembly, each of said headers being formed by a structure providing header connections with said annular passageways for one fluid circuit and header connections with said central passageways for another fluid circuit, one of said fluid circuits providing the evaporator for said refrigerator system, and the other of said fluid circuits providing for the introduction of a heated fluid to perform the defrosting operation.

CECIL BOLING.

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